TRANSIENT ABSORPTION SPECTROMETER FOR THE PICOSECOND TIME RANGE

A new experimental solution of a picosecond transient absorption spect rometer with a high power pulse YAG:Nd+3 laser, YG 571C type (Quantel) , has been described and tested. The system has been designed to study photophysical and spectral properties of molecular systems. The excit ation is realized with the second, third and fourth harmonics of the b asic YAG:Nd+3 laser frequency of the maximum energies of 30, 10 and 4 mJ, respectively, the pulse width of similar to 15 ps (fwhm) and the r epetition rate of 10 Hz. The analysing beam is the ''white'' light of the picosecond continuum generated by the 1064 nm beam in isopropanol. The optical delay line of 20 cm travel range permits investigation of the processes occurring in the time scale to 1.3 ns with the time ste p of similar to 3 fs. Autocorrelation measurements of two-photon fluor escence excitation were performed in the system in order to determine the instrument response function The zero-point position was found fro m the T-1-T-g transient absorption measurements in benzophenone/hexane solution. The system was used to study the interaction of the excited xanthione molecules with alkanes and benzene occurring in the picosec ond time scale. The sensitivity of the system permits measurements of transient absorption in a sample of a molar extinction coefficient sim ilar to 500 M(-1) cm(-1) with the actual time resolution of similar to 1 ps.